Introduction

Indoor air pollution refers to the occurrence of contaminants within a home, workplace (or other inhabited enclosure) arising from such sources as fuel combustion for heating or cooking; from stored substances, furnishings and carpeting; or from the particular geology (underlying rocks) of an area.

As cited by the Indian Council of Medical Research (ICMR) Bulletin, the report of the World Health organization (WHO) emphasizes the ‘rule of 1000’ which states that when a pollutant is released indoors, it is one thousand times more likely to reach people’s lungs than a pollutant released outdoors [1]. More than 1.6 million people, mainly women and children, die prematurely each year after breathing high levels of indoor smoke. This represents approximately twice the estimated mortality due to outdoor pollution [2]. Children and senior citizens can be more vulnerable to indoor pollution because their immunity may be compromised.

The quality of indoor air can affect the health, safety and comfort of occupants. Indoor air problems can be subtle and do not always produce easily recognized impacts on health. Nonetheless, poor indoor air quality gives rise to demonstrated short- and long-term health problems [3]. Significantly, people in general spend approximately 90% of their time breathing indoor air. There is little question, therefore, that we need better science-based information focusing on source characteristics as well as on health effects and consequences of indoor air pollution—so as to avoid and mitigate unnecessary health and environmental outcomes.

Sources of Indoor pollutants

Sources of indoor air pollutants can originate within any relatively enclosed structure (for example, an office building, a single family dwelling); of course, problematic pollutants can be drawn indoors from outdoor sources. Since indoor air is recycled over and over, it can trap and accumulate pollutants.

Among all the indoor air pollutants, persistent organic pollutants (POPs) persist in the environmental media and are extremely lethal even in small amounts [5]. Exposure to POPs is recognized as an important environmental risk factor for humans causing cancer, nervous system damages, reproductive and immune system impairments [5]. Once released from the sources, they can remain unaltered and persist in the environment for long periods because of their extensive half-life. They are lipophilic, bioaccumulate in organisms (in their fatty tissue) and may then build up in food chains (biomagnification). In addition to that, POPs can reach organisms through the long-range transport mechanisms crossing regional and national boundaries [6,7].

Biological contaminants like bacteria, molds, viruses and yeasts are usually found in moist indoor environments. They can also act as human pathogens. Their potential health effects include allergies, irritation and sensitivity (because of volatile organic chemicals, VOCs, produced during metabolism) and toxicity (due to mycotoxins produced by molds). Molds can cause major structural damage and may lead to financial losses. There have been reports of severe illness as a result of indoor mold exposure, particularly due to Stachybotryschartarum, a toxic black mold [8].

Dilution of indoor pollutants with outdoor air is effective to the extent that outdoor air is free of harmful pollutants. There is strong evidence to demonstrate the association between ventilation, air movement in buildings and the transmission or spread of such infectious diseases as measles, tuberculosis, chickenpox, influenza, smallpox and severe acute respiratory syndrome (SARS) [9]. In addition, the odors may result in psychological effects and disruption in work.

Indoor air pollution is a major health concern in today’s globalised world. In many developed countries, energy efficiency improvements sometimes make habitations comparatively airtight—with reduced levels of fresh air and elevated levels of pollutants [10]. On a global scale, the use of solid fuels for cooking and heating is likely to be the largest source of indoor air pollution. In developing countries, most indoor air pollutants originate from the combustion of unprocessed solid biomass fuels like wood, dung, coal and crop residues used by poor urban and rural folk for cooking and heating [4]. Approximately, 90% of rural households in developing countries still rely on such fuels [11]. Burning such fuels produces a large amount of smoke and other air pollutants in the confined space of the home, resulting in relatively high exposure levels.

Consequences of Indoor Air Pollution Exposure

Health effects from exposure to indoor air pollutants may be experienced soon after exposure or even in some cases after many months or years [1]. Also, immediate effects may show up after a single exposure or after repeated exposures including irritation of the eyes, nose and throat, headaches, dizziness and fatigue. Such symptoms of diseases as asthma may occur soon after exposure to indoor air pollutants. Increases in the incidence of asthma and allergies worldwide during recent years have stimulated research on potential environmental causes [12].

The occurrence of respiratory and pulmonary diseases is the most common outcome of the indoor air pollutants. The most commonly reported health effects of indoor air pollutants are acute respiratory infections (ARIs), especially childhood ARIs, that are the single most important cause of mortality in children aged less than 5 years, responsible for between 1.9 million and 2.2 million children deaths annually in this age group globally [12]. Women and children in rural areas of developing countries are exposed often to high levels of pollutants from biomass combustion that is associated with a range of respiratory symptoms. According to a report by Ghosh et al. (2011), the chemicals resulting from combustion of coal may form residues on household surfaces and food.

Children raised in homes using indoor coal for cooking or heating appear to be about a half-inch shorter (skeletal growth impairment) at age 36 months than those in households using other fuel sources [13]. In developed countries, smoking is responsible for over 80% of cases of chronic bronchitis (inflammation and swelling of the lining of the airways leading to its narrowing and obstruction), emphysema (damage of lung alveoli characterized by breathing difficulty) and chronic obstructive pulmonary disease (characterized by wheezing, chronic cough and breathing difficulty) [2].

Indoor air pollutants (from cooking for instance), results in exposure of the eyes to the radiating smoke containing toxins that are absorbed by the lens of the eyes. This results in the opacity of the lens. The prevalence of cataracts is higher in females than in males in developed and developing countries [14,15] and in developing countries cataracts occurs at an earlier age [16]. Contact with indoor air pollutants (for example, CO) can also result in adverse pregnancy outcomes; still births and low birth weight (LBW). LBW has severe effects including increased mortality during infancy [17].

Another set of health problems associated with time spent in a building are commonly referred to as Sick Building Syndromes (SBSs) [3]. Common related symptoms include, eye, nose and throat irritation; mental fatigue; headaches; airway infections; coughing; wheezing; and nausea. SBS has been described as having three or more above mentioned symptoms. The common causes of SBS include inadequate ventilation and contaminants from various sources.

Often, it is difficult to determine which pollutants are the causes of poor health even if indoor pollution is the problem. Many indoor air pollution sources cannot be detected by our senses and the symptoms they produce can be vague, making it hard to attribute them to a specific cause. Some symptoms may take weeks or even months—even years—to develop, making it even harder to determine the cause.

Preventing Indoor Air Pollution

Basic approaches to eliminate indoor air pollution include:

source control (a preventive technique; for example, banning smoking in public areas) and source isolation (when source can not be removed; for instance, separate venting of bathrooms); and

increased ventilation and dehumidification to facilitate the reduction of microbial growth.

However, indoor pollution may be decreased by properly identifying and eradicating the sources.

Measures to control indoor air pollution can be summed up as [1]:

Educating the public: Public education is valuable in preventing illnesses resulting from combustion of biomass fuels to ensure awareness of the long-term health effects of indoor air pollution. Also, awareness campaigns should be organized in schools and villages so that the most vulnerable populations (that is, the elderly, women and children) can be targeted.

Workers and working conditions surveillance: Workplace and the workers should be thoroughly evaluated for problem identification and correction. If, after the remedial action, the illness persists in the workplace, the affected person should be considered for permanent reassignment to another area.

Choice of fuel: The choice of fuel for domestic energy can be associated with such factors as availability of fuel, affordability and habit of the user. Around 50% of people in developing nations rely on coal and biomass for energy requirements.

Cooking stove: Incomplete combustion due to inadequate design of the stove leads to enormous emissions. Efforts should be made to modify stove designs to make them fuel efficient and provide them with a ventilation mechanism (e.g. chimney) to remove pollutants from the indoor environment.

Ventilation: Ventilation ensures mixing of the outside air with indoor environment to reduce accumulation of indoor pollutants.

Elimination of the sources of microbial contaminants: Regular clean-up and repair of all areas where water leakage has occurred including floors, roofs and drains helps to ensure removal of microbial habitats. Feathered pets should be restricted to less occupied parts of the home. Washing cats and dogs can reduce allergen levels for a few days.

Conclusions

Indoor air pollution is responsible for a high degree of morbidity and mortality warranting immediate steps for intervention by the general public and the policy makers.

It is caused by burning traditional fuels such as dung, wood and crop residues and causes considerable damage to the health particularly of women and children. Cataract and adverse pregnancy outcome (LBW and still births) are conditions shown to be associated with the use of biomass fuels.

People who may be exposed to indoor air pollutants for the longest periods of time are often those most susceptible to the effects of indoor air pollution. Such groups include the young children, the elderly, and the chronically ill, especially those suffering from respiratory or cardiovascular disease. While pollutant levels from individual sources may not pose a significant health risk by themselves, most houses have more than one source that contributes to indoor air pollution. There can be serious risks from the cumulative effects of these pollutants.

The first and the most important step in the prevention of illness caused by the indoor air pollution is to educate the public and the policy makers to eradicate the problem form the grass root level. Systematic data about actual exposure levels to indoor air pollutants experienced by people should be collected. Awareness programs should, therefore, be undertaken to reduce indoor pollutants.

References

1.Indoor air pollution in India – a major environmental and public health concern. ICMR Bulletin 31(5), May, 2001.

17.Indoor air pollution from solid fuels and risk of low birth weight and stillbirth Report from a symposium held at the Annual Conference of the International Society for Environmental Epidemiology (ISEE), September 2005, Johannesburg, South Africa, WHO, available online http://www.who.int/child_adolescent_health